1. Field of the Invention
This invention relates to devices that undergo an optical change and, in particular, devices that undergo an optical change due to application of an electric field.
2. Art Background
Many classes of devices that undergo a color change upon application of a voltage have been extensively investigated. For example, light-emitting diodes and liquid crystal devices are now widely used in a variety of products. Despite the predominant use of light-emitting diodes and liquid crystal devices many other classes of devices that undergo an optical change are being investigated. This continued investigation indicates the tremendous demand for such devices.
One type of device presently being investigated is based on the electrophoretic effect. In these devices a white material is suspended in a colored supporting medium. For example, white pigmented particles are suspended in a blue liquid. The medium with its suspended particles appears to be blue. However, the particles are chosen so that they respond to an electrostatic charge. Such a charge is developed on the electrodes. This charge attracts the white particles that, in essence, plate the area where the complementary charge is located and cause the cell to appear white. Initially, these devices seemed promising because of their pleasing esthetics. However, use of electrophoretic is quite limited since there is a tendency for the suspended particles to flocculate or to precipitate. Thus, the life of these devices are typically too short for many applications. Additionally, relatively large potentials, e.g., approximately 30 V or greater, are necessary to attain response times of 100 msec. or less.
Although some devices have generated only modest interest for display applications, others have had phenomenal commercial success. Research for other suitable device configurations is thus still being vigorously pursued.